Six complementary and collaborative projects are proposed, with a common scientific and administrative core, to elucidate the nature and emergence of cognitive competence as it is manifest across human and nonhuman primate species, across developmental periods, and across different groups (e.g., individuals with ADHD). The present application benefits from substantial collegiality between investigators and convergence between the projects, so that the scientific promise of the entire program greatly exceeds the sum of the anticipated scientific gains of each strong individual project. The psychological processes being investigated (learning, memory, attention, executive function, categorization, language, and self regulation) are themselves closely inter-related, such that understanding of any one process dictates studying its relation to the other constructs using behavioral, cognitive, comparative, developmental, and neuroscientific paradigms. The application reflects a wide range of converging measures, including task performance, brain imaging, genetic analyses, and psychophysiology. The goal of these projects is to build on the current state of knowledge, including the recent findings from our own research, and to inform and be informed by theories regarding behavior and its interaction with experience and biology. RELEVANCE: The findings of these projects will advance our understanding of cognition and its disorders, generating educational interventions and clinical applications with relevance to a wide range of mental health issues.